Chip carrier used for semiconductor optical device, optical module, and optical transmitter and receiver

ABSTRACT

A chip carrier includes a metal-coated portion formed on a front surface of a substrate and to be mounted a device, and a rear surface of the substrate being coated with a metal, in which a metal-coated portion is formed on a side surface of the substrate and the metal-coated portion on the front surface of substrate is connected with the metal-coated portion on the rear surface by the metal-coated portion formed on the side surface of the substrate, thereby maintaining frequency characteristics of the optical semiconductor device.

This application relates to Japanese Patent Application No. 2003-432013filed on Dec. 26, 2003, the entire disclosure of which is incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a chip carrier incorporating an opticalsemiconductor device or the like mounted thereon, an optical moduleusing this chip carrier, and an optical transceiver.

2. Description of the Related Art

In general, an optical module is formed by incorporating a chip carrieron which an optical semiconductor device or the like such as asemiconductor laser diode (hereinafter, referred to as an LD) is mountedby soldering those onto a package including a power supply terminal, aninput signal terminal, a ground terminal, an optical output fiberconnector terminal and the like. As the chip carrier, there is used adielectric material or a semiconductor substrate. The opticalsemiconductor device is mounted on a ground metal-coated portion, bysoldering, formed on the surface of the dielectric material orsemiconductor substrate, and the optical semiconductor device is thenconnected with a high-frequency transmission line or the like formed onthe same substrate surface through wire-bonding.

With increase of operating speed in relation to the opticalsemiconductor device in recent years, excellent high-frequencycharacteristics have also been demanded with respect to the chipcarrier. As a structural example of the chip carrier aiming at animprovement in the high-frequency characteristics, JP-A-10-275957discloses a structure in which a conductive substrate having an opticalsemiconductor device mounted thereon is incorporated with a dielectricmaterial or a semiconductor substrate having a high-frequencytransmission line and a terminating resistor arranged thereon.

In an ordinary chip carrier using only a dielectric material or asemiconductor substrate, excellent characteristics are hard to beobtained in a high-frequency domain of 20 GHz or above.

Further, in such a chip carrier in which the conductive substrate andhigh-frequency transmission substrate are separately provided asdisclosed in JP-A-10-275957, although high-frequency characteristics arerelatively good, there is a problem that its manufacturing cost is highbecause of its structure, and a packaging process requires much time.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a chip carrier thatis superior in the high-frequency characteristics and has a low cost, anoptical module incorporating this chip carrier assembled therein, and anoptical transceiver.

To achieve this object, reduction of an inductance on the chip carrieris a dominant means. That is, a high-frequency transmission line and aground metal-coated portion are arranged on a dielectric material or asemiconductor substrate, a rear surface of which is coated with a metal;the metal-coated portion on the front surface are electrically connectedwith the metal-coated portion on the rear surface through a metallicvia-hole; a part or all of a side surface of the chip carrier is coatedwith a metal; and the metal-coated portion on the front surface of thedielectric material or the semiconductor substrate is electricallyconnected with the metal-coated portion on the rear surface.

Furthermore, as another means for reducing an inductance of the chipcarrier, the reduction of distance between the optical semiconductordevice mounted on the chip carrier and the via-hole of the chip carrieris also prevailing means. In the present invention, when distancebetween the positions of the optical semiconductor device and thevia-hole is relatively close in minimum, that is, the via-hole isarranged directly below the optical semiconductor device.

Thereby, using the chip carrier according to the present invention doesnot deteriorate the frequency characteristics of optical semiconductordevice operating at a high speed. Furthermore, the chip carrier in lowcost, an optical module incorporating the chip carrier and an opticaltransceiver are realized.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are plane and side views illustrating a chip carrierstructure according to the present invention;

FIGS. 2A and 2B are diagrams illustrating characteristics obtained bythe chip carrier according to the present invention;

FIG. 3 is a diagram showing an equivalent circuit of the chip carrieraccording to the present invention;

FIG. 4 is a plane view illustrating a chip carrier structure accordingto the present invention;

FIG. 5 is a diagram illustrating characteristics obtained by the chipcarrier according to the present invention;

FIG. 6 is a diagram illustrating an LD module structure according to thepresent invention;

FIG. 7 is a diagram illustrating characteristics obtained by the LDmodule according to the present invention;

FIG. 8 is a plane view illustrating a chip carrier structure accordingto the present invention; and

FIG. 9 is a diagram illustrating characteristics obtained by the chipcarrier according to the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments according to the present invention will be described indetail hereinafter.

Embodiment 1

FIGS. 1A and 1B show an upper surface and a side surface of a chipcarrier 100 in a first embodiment according to the present invention.The chip carrier 100 uses a substrate 101 comprising a dielectricmaterial such as alumina (AlN) or a semiconductor formed of silicon(Si). The following elements are then formed on the substrate: ahigh-frequency transmission line 102; a ground metal-coated portion 103on which an optical semiconductor device is mounted; and a terminatingresistor 104. The optical semiconductor device 110 is soldered on theground metal-coated portion 103. In this embodiment, a description willbe given on the assumption that an external modulator integrated laserincorporating a semiconductor laser 111 and an external modulator 112 isused as the optical semiconductor device 110.

In this embodiment, the high-frequency transmission line 102 is amicro-strip line, and the ground metal-coated portion 103 iselectrically connected with a metal-coated portion on a rear surfacethrough a via-hole 105.

It is noted that reference numeral 106 denotes a lead wire connected toa direct-current power source; 107, a lead wire connected themicro-strip line with the external modulator 112; and 108, a lead wireconnecting the external modulator 112 with a high-frequency lineconnected to the terminating resistor 104.

In the present invention, a part (120) or all side surfaces of thesubstrate 101 is coated with a metal, and a metal-coated portion 103 onthe front surface of the substrate is electrically connected with ametal-coated portion on the rear surface of the same in order to enhancethe ground. It is noted that coating with a metal on a side surface 150placed at a position closest to a modulator 112 directly concerning ahigh-frequency operation is most effective, among four side surfaces 150to 153 of such a chip carrier as shown in FIG. 4.

In order to confirm an effect of the present invention, FIG. 2A showsoptical response characteristics obtained by an actual device mounted onthe chip carrier (in a case where the side surface 150 is entirelycoated with a metal) according to this embodiment. It is noted that theoptical response means a ratio of an output light intensity relative toa high-frequency signal intensity input to the modulator. For thepurpose of comparison, FIG. 2B shows characteristics obtained when theside surface is not coated with a metal.

When the side surface is not coated with a metal (FIG. 2B), thecharacteristics are abruptly deteriorated in the vicinity of 35 GHz, anda resonance is also produced. On the contrary, when the side surface 150is entirely coated with a metal (FIG. 2A), an abrupt deterioration inthe characteristics and the resonance do not occur, and the opticalresponse of −3 dB is obtained even in the vicinity of 40 GHz, realizingthe excellent high-frequency characteristics.

FIG. 3 shows an equivalent circuit when the external modulation typelaser is mounted on the chip carrier. Here, reference numeral 301denotes a characteristics impedance of the high-frequency transmissionline 102, i.e., 50 Ω; 309, a resistance Rt of the terminating resistor104, i.e., 50 Ω; 302, an inductance L1 of a bonding wire 108; 303, aninductance L2 of a bonding wire 109; 304, an internal resistance Rm ofthe modulator 112; 305, a parasite capacitance Cm of the modulator 112;306, a resistance Rc of the chip carrier 100; 307, a capacitance Cc ofthe chip carrier 100; and 308, an inductance Lc of the chip carrier 100.

It is noted that a laser 111 of the external modulator integrated laseris of a direct-current drive type, and the equivalent circuit of thelaser portion can be ignored in analysis of the high-frequencycharacteristics. Therefore, FIG. 3 shows only the modulator portion inthe equivalent circuit.

The abrupt deterioration in characteristics or the resonance in thevicinity of 35 GHz observed in FIG. 2B is caused by a series resonancedue to the parasite capacitance Cm of the modulator 112 and theinductance Lc of the chip carrier 100. Here, a resonance frequency fr isgiven by the following expression.${fr} = \frac{1}{2\pi\sqrt{{Lc} \cdot {Cm}}}$

In order to improve the characteristics by shifting this seriesresonance frequency to the high-frequency side, the parasite capacitanceCm of the modulator must be reduced or the inductance Lc of the chipcarrier must be decreased. However, the capacitance reduction of themodulator may possibly occur deterioration in device characteristicssuch as a drop in an extinction ratio that is a ratio of ON/OFF of lightbeams. Therefore, it can be considered that the inductance reduction ofthe chip carrier is dominant means.

In the structure of FIG. 1, the inductance Lc of the chip carrier isreduced by coating with the metal on the side surface of the chipcarrier and enhancing the ground, sufficiently increasing the seriesresonance frequency. For this reason, it can be considered that theexcellent optical response characteristics is obtained without such anabrupt deterioration in characteristics or a resonance as shown in FIG.2A.

It is noted that the characteristics differs depending on the area ofthe side surface coated with the metal. FIG. 5 shows a simulation resultof frequency characteristics (transmission characteristics) when{fraction (1/10)}, ⅕, ⅓, ½ and all of a superficial content of the sidesurface 150 is coated in cases where the side surface 150 of the chipcarrier which is closest to the modulator portion 121 is coated with ametal.

It can be understood from the simulation result of FIG. 5 that thefrequency characteristics are improved by increasing a metal-coatedarea. In particular, in a domain of 40 GHz or above, it can be revealedthat the characteristics substantially equivalent to those, when theentire surface is coated with a metal, can be obtained by setting themetal-coated area to ⅓ or above.

FIG. 6 is a structural diagram of an LD module 600 incorporating thechip carrier according to this embodiment. A high-frequency signal 630is supplied from the outside to the optical semiconductor device 110 onthe chip carrier 100 through a relay substrate 602. Likewise, adirect-current power 640 for driving the optical semiconductor device110 is supplied through a relay substrate 603. Laser beams 610 from theoptical semiconductor device 110 are condensed by a condenser lens 601,and transmitted to an optical transmission fiber 620 connected to theoutside. Moreover, in order to monitor an optical output state of theoptical semiconductor device 110, a monitor photodiode 604 is mounted.

FIG. 7 shows optical response characteristics obtained from an actualdevice when the side surface of chip carrier 100 is coated with a metalin the LD module depicted in FIG. 6. It is noted that the side surfaceof the optical semiconductor device 110 closest to the modulator 112 isentirely coated with a metal. For a purpose of comparison, opticalresponse characteristics of the LD module incorporating a chip carrier,the side surface of which is not coated with the metal mounted thereonare also shown. It was ensured from this evaluation result that coatingthe side surface of the chip carrier results in an improvement of theoptical response characteristics by approximately 10 GHz.

As described above, according to this embodiment, simply coating theside surface of inexpensive conventional chip carrier constituted of thedielectric material or semiconductor substrate with the metal can obtainthe excellent frequency characteristics without the abrupt deteriorationin the characteristics, and it is possible to provide the chip carrierwhich is inexpensive, has easy operating steps and is superior infrequency characteristics, the optical module using this chip carrier,and the transceiver.

It is noted that the description has been given as to the case using theexternal modulator integrated laser as the optical semiconductor devicein this embodiment, the same effect can also be expected even if thedirect-modulated laser having no external modulator is used. In thiscase, the side surface closest to the position of chip carrier on whichthe directed-modulated laser is mounted is coated with the metal.

The present invention is not restricted to shapes or properties ofconstituent components on the chip carrier. For example, although thehigh-frequency transmission line is a micro-strip line in thisembodiment, the respective similar effects can be demonstrated in caseof a line (generally, a line of 50 Ω) which does not attenuate ahigh-frequency signal such as a coplanar line or a grounded coplanarline (coplanar line having a rear surface of the substrate coated with ametal).

Embodiment 2

It has been apparent from the foregoing embodiment that reducing aninductance of the chip carrier is important in order to improve thehigh-frequency characteristics of the chip carrier. Here, there can beconsidered the reduction of distance between the modulator 112 of theexternal modulator integrated laser 110 mounted on the chip carrier andthe via-hole of the chip carrier as another means for reducing theinductance. In order to reduce this distance to the minimum level, it isgood enough to arrange the via-hole 105A directly below the modulator112 as shown in FIG. 8. Reference numerals excluding the via-hole 105Adenote structures identical to those described in conjunction with FIG.1A.

FIG. 9 shows a simulation result of frequency characteristics when thevia-hole 105A is arranged directly below the modulator 112 depicted inFIG. 8. As compared with the example in which the side surface of chipcarrier is coated with the metal described in conjunction with the firstembodiment, it is apparent that the excellent characteristics that aresonance does not occur in a high-frequency domain can be obtained.

However, the flatness of a via-hole portion and the dielectric materialor the semiconductor substrate around this portion may be deterioratedwhich results in reducing adhesive property at the time of soldering thedevice by arranging the via-hole directly below the device in somecases. Additionally, there is possibility that stress may be applied tothe optical semiconductor device due to a different thermal expansioncoefficient between the via-hole portion and the substrate and therebythe reliability of the device may not be guaranteed. Therefore, acountermeasure against these deteriorations, e.g., reinforcement ofsoldering is additionally applied according to needs.

As described above, according to this embodiment, in the inexpensiveconventional chip carrier comprising the dielectric material orsemiconductor substrate, since the excellent frequency characteristicswithout the abrupt deterioration or resonance in characteristics can beobtained by simply changing the position of via-hole thereof, it ispossible to provide a chip carrier which is inexpensive, has easyoperating steps and is superior in frequency characteristics, theoptical module using this chip carrier, and the optical transceiver.This embodiment is not restricted to shapes or properties of constituentcomponents on the chip carrier like the first embodiment.

Moreover, a further improvement in the high-frequency characteristicscan be expected by conformation in which the first embodiment iscombined with this embodiment, i.e., coating the side surface of chipcarrier with the metal and providing the via-hole directly below theoptical semiconductor device which is operated with a high frequency.

It is noted that the description has been given as to the example inwhich the external modulator integrated laser is used as the opticalsemiconductor device in this embodiment, but the same effect can beexpected even if a direct-modulated laser having no external modulatoris used. In such a case, the via-hole is arranged directly below aposition of the chip carrier at which the direct-modulated laser ismounted.

Although a light emitting device has been described in both the firstembodiment and the second embodiment, the present invention is notrestricted thereto, and it is also effective to a chip carrier of adetector such as a photo diode (PD) or an avalanche photo diode (APD),an optical module using this chip carrier, and a PD receiver.

It is also effective to an optical transceiver which both the LD moduleand the PD module mentioned above are incorporated in the same package.

Further, the chip carrier according to the present invention is notrestricted to the optical semiconductor device. An improvement inhigh-frequency characteristics can be expected by using the chip carrieraccording to the present invention as long as it is a device in which afactor deteriorating high-frequency characteristics is caused by aparasite capacitance of the device, i.e., a capacitive device having acapacitor structure such as a transistor.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

1. A chip carrier including a metal-coated portion formed on a front surface of a substrate and to be mounted a device, and a rear surface of the substrate being coated with a metal, wherein a metal-coated portion is formed on a side surface of the substrate, and wherein the metal-coated portion on the front surface of substrate is connected with the metal-coated portion on the rear surface by the metal-coated portion formed on the side surface of the substrate.
 2. The chip carrier according to claim 1, wherein the metal-coated portion on the front surface of the substrate is connected with the metal-coated portion on the rear surface by a metallic via-hole formed on passing through the substrate.
 3. A chip carrier including a metal-coated portion formed on a front surface of a substrate and mounted an optical semiconductor device, and a rear surface of the substrate being coated with a metal, wherein a metal-coated portion is formed on a side surface of the substrate, and wherein the metal-coated portion on the front surface of substrate is connected with the metal-coated portion on the rear surface by the metal-coated portion formed on the side surface of the substrate.
 4. The chip carrier according to claim 3, wherein the metal-coated portion on the front surface of the substrate is connected with the metal-coated portion on the rear surface by a metallic via-hole formed on passing through the substrate.
 5. The chip carrier according to claim 3, wherein the metal-coated portion formed on the side surface of the substrate is formed on the side surface closest to a position at which the optical semiconductor device is mounted.
 6. The chip carrier according to claim 5, wherein an area of the metal-coated portion formed on the side surface of the substrate is equal to or greater than ⅓ of the side surface.
 7. An optical module incorporating a chip carrier with an optical semiconductor device mounted, wherein the chip carrier including a substrate, a rear, a front and a side surfaces of the substrate being coated with a metal, and the optical semiconductor device being mounted on the metal-coated portion of the front surface, and wherein the metal-coated portion on the front surface of the substrate is connected with the metal-coated portion on the rear surface by the metal-coated portion formed on the side surface of the substrate.
 8. The optical module according to claim 7, wherein the metal-coated portion on the front surface of the substrate of the chip carrier is further connected with the metal-coated portion on the rear surface by a metallic via-hole formed on passing through the substrate.
 9. The optical module according to claim 7, wherein the metal-coated portion formed on the side surface of the substrate of the chip carrier is formed on the side surface closest to a position at which the optical semiconductor device is mounted.
 10. The optical module according to claim 9, wherein an area of the metal-coated portion formed on the side surface of the substrate of the chip carrier is equal to or greater than ⅓ of the side surface.
 11. A chip carrier including a metal-coated portion formed on a front surface of a substrate and mounted an optical semiconductor device, and a rear surface of the substrate being coated with a metal, wherein the metal-coated portion on the front surface of the substrate is connected with the metal-coated portion on the rear surface by a metallic via-hole formed on passing through the substrate, and wherein the via hole is formed below the optical semiconductor device.
 12. The chip carrier according to claim 11, wherein a metal-coated portion is formed on a side of the substrate, and wherein the metal-coated portion on the front surface of the substrate is further connected with the metal-coated portion on the rear surface by the metal-coated portion formed on the side surface of the substrate.
 13. An optical module incorporating a chip carrier with an optical semiconductor device mounted, wherein the chip carrier includes a substrate, a rear and a front surfaces of which are coated with a metal, and the optical semiconductor device being mounted on the metal-coated portion on the front surface, wherein the metal-coated portion on the front surface of the substrate is connected with the metal-coated portion on the rear surface by a metallic via-hole formed on passing through the substrate, and wherein the via-hole is formed below the optical semiconductor device.
 14. The optical module according to claim 13, wherein a metal-coated portion is formed on a side of the substrate, and wherein the metal-coated portion on the front surface of the substrate of the chip carrier is further connected with the metal-coated portion on the rear surface by the metal-coated portion formed on the side surface of the substrate.
 15. An optical transceiver incorporating an optical module constituted of chip carriers on which optical semiconductor devices are mounted, respectively wherein each of the chip carriers for transmission and reception includes the optical semiconductor device mounted on a metal-coated portion formed on a front surface of a substrate, a rear and a side surfaces of which are coated with a metal, and wherein the metal-coated portion on the front surface of the substrate is connected with a metal-coated portion on the rear surface by the metal-coated portion formed on the side surface of the substrate.
 16. An optical transceiver incorporating an optical module constituted of chip carriers on which optical semiconductor devices, respectively are mounted, wherein each of the chip carriers for transmission and reception includes the optical semiconductor device mounted on a metal-coated portion formed on a front surface of a substrate, a rear side surface of which is coated with a metal, wherein the metal-coated portion on the front surface of the substrate is connected with the metal-coated portion on the rear surface by a metallic via-hole formed on passing through the substrate, and wherein the via-hole is formed below the optical semiconductor device. 